In numerous processes in the chemical industry, fluid streams occur containing acid gases, for example CO2, H2S, SO2, CS2, HCN, COS or mercaptans, as impurities. These fluid streams can be, for example, gas streams (such as natural gas, synthesis gas or heavy oil or heavy residues, refinery gas, or reaction gas resulting from the partial oxidation of organic materials, for example coal or petroleum) or liquid or liquefied hydrocarbon streams (such as liquefied petroleum gas “LPG”) or natural gas liquids (“NGL”).
Before these fluids can be transported or further processed, the acid gas content of the fluid must be significantly decreased. For example, CO2 must be removed from natural gas since a high CO2 concentration decreases the heating value of the gas. In addition, CO2, in combination with water entrained in a fluid stream can lead to corrosion on pipelines and fittings.
The removal of sulfur compounds from these fluid streams is also of particular importance. For example, the content of sulfur compounds of natural gas must be reduced by suitable treatment measures directly at the natural gas source, since the sulfur compounds can also form corrosive acids in the water entrained in the natural gas. Furthermore, numerous sulfur compounds are foul smelling, even at low concentrations, and can be toxic.
Processes have been developed for removing acid gas constituents from fluid streams such as hydrocarbon gases, LPG, or NGL. In most processes, the fluid mixture containing the acid gas constituents is brought into contact with absorbent solvents in a gas scrubber or a liquid/liquid extraction stage.
On an industrial scale there are primarily two categories of absorbent solvents depending on the mechanism to absorb the acidic components: chemical solvents and physical solvents. Each solvent has its own advantages and disadvantages as to features such as loading capacity, kinetics, regenerability, selectivity, stability, corrosivity, heat/cooling requirements, etc.
Physical solvents which have proven to be industrially suitable are cyclo-tetramethylenesulfone and its derivatives, aliphatic acid amides, N-methylpyrrolidone, N-alkylated pyrrolidones and the corresponding piperidones, methanol, ethanol, and mixtures of dialkylethers of polyethylene glycols.
Chemical solvents which have proven to be industrially useful are primary, secondary and/or tertiary amines derived from alkanolamines. The most frequently used amines are derived from ethanolamine, such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA), monomethyl ethanolamine (MMEA), piperazine and methyldiethanolamine (MDEA).
A particularly effective absorbent solution is one that contains 2-(2-aminoethoxy)ethanol. However, 2-(2-aminoethoxyethanol) can form into morpholine which is removed in the stripper section of a gas treating system. Thus, this compound must either be replaced or regenerated periodically to retain efficiency. Accordingly, it is highly desirable to develop alternative absorbent solutions which are as highly effective yet overcome the problem described above.